Linear accelerators (LINACs) are used to produce high energy radiation beams useful in radiation therapy and imaging of patients and in other applications such as safety inspection. A linear accelerator includes various devices operable to produce, condition, or monitor radiation beams. By way of example, an x-ray target produces x-rays upon impingement by energetic electrons. A beam filter such as a photon flattening filter conditions x-rays to provide a desired energy or dose distribution profile across the radiation field. In an electron mode operation of a linear accelerator, a scattering foil and button is used to scatter incident electrons to provide a broadened, uniform beam profile.
In conventional linear accelerators, full sized beam filters are used in filtration of x-ray beams of different energy levels. For x-ray beams of high energy levels such as 18 MV, 20 MV or higher, a beam filter may be composed of multiple materials to create a desired filtration. The use of full sized beam filters for radiation beams of different energy levels requires greater filter material volumes and sizes and increases manufacturing costs.
Conventional beam filter positioning devices include exchangers which are designed to carry full sized beam filters and allow switching of individual filters for beams of different energy levels. For example, a conventional carousel exchanger is designed to carry five full sized individual filters for filtration of beams of five different energy levels. This kind of positioning device design requires more space or clearance for full sized filters' movement and more complicated motion axes for positioning and retracting beam filters in and/or out of the beam path.